Pruning Indeterminates for Cordon Growth

Let’s start with the least contentious type of pruning - the growing of cordons. A cordon is a plant which has been trained to grow as one stem (or several chosen stems), with leaves and trusses at the usual intervals. Indeterminate tomatoes are great for this, since they are essentially vines and given the opportunity, will grow like weeds! This means that one growth tip is all you need; the plant will keep on going in one direction until conditions force it to stop. There are lots of good reasons to grow indeterminates in this way, especially in the UK, but it is worth noting that in other climates, when grown outdoors in hot, dry conditions, many growers do not prune their indeterminates at all, but rather support the full growth of the plant using trellises, wires or cages. This has many benefits, not least a much increased crop, but is rarely possible in the UK, although this style of growing may become more viable with the changing climate and heatwaves we have seen in 2025!

Cordons in the polytunnel

Small sideshoots - the ideal time to remove them

Why train tomatoes as cordons?

The UK’s climate is unpredictable, as we all know. We are known all over the world for talking about the weather! Growing tomatoes outdoors can be a bit of a challenge, some years it is simply too cold to get a good crop, or so damp that blight or other fungal diseases take hold before the majority of the fruit ripen. Outdoor growing is certainly possible, and there are varieties that have been bred specifically to grow and ripen well in cooler climates. However, it can feel unreliable and be very disheartening in a bad year.

For consistency of growing conditions, and the added heat, many growers choose to use polytunnels and greenhouses. This gives us a bit more control, we can choose when to water, and how much, whether to increase or reduce ventilation, add or remove shade etc. The downside is that if you don’t keep the plants under control, by July you won’t be able to get through the door!

Indeterminate plants grow from growth tips, which multiply exponentially. A young plant only has one growth tip, this is known as your main leader. This is the stem that you want to maintain and support throughout the plant’s life. If you want to grow a cordon in an indoor space, this means removing other potential leader-stems.

When the plant reaches about a foot tall, it will start to produce sideshoots - new leaders that grow from the space between the main stem and leaf stems. Left unchecked, each sideshoot will turn into a new leader, growing in a different direction. All side shoots can and will produce flowers and fruit, so the temptation of extra yeild is hard to resist. Pinching out sideshoots can feel ruthless and brutal!

Not removing sideshoots, however, will lead to a very large and unruly plant, which is fine if you are growing them somewhere with a lot of space. There is a myth that allowing sideshoots to grow means that the plant is focussing on foliage, and not on producing fruit. This is not true - sideshoots will flower and produce fruit in the same was as the normal stem. The quality and size of the fruit is not diminished by allowing extra growth; it can seem like this is the case, but actually the cause of this problem is insufficient watering and feeding for the size of the plant, especially if plants are grown in pots or grow bags.

For greenhouse or polytunnel growing, I advise leaving a maximum of 2 or 3 leaders per plant, and if you intend to do that, planting with a minimum of 2ft between each plant. For outdoor growing, if you choose to, you can be more relaxed about the pruning of sideshoots, as long as you make sure to maintaing watering and feeding regimes. Just don’t let the plants get too dense as to impact airflow - this will help to keep fungal diseases at bay.

Showing a large sideshoot, which can be removed at the blue line

Pruning of Lower Leaves

Indeterminate tomatoes are vines, this means they grow sequentially, from one end to the other, putting new growth at the top, and slowly using up the leaves at the bottom. If left undistrubed, the lower leaves will gradually degrade, eventually turning yellow and dropping off. These degrading leaves are perfectly natural, and separate from the plant at the abscission layer - a layer of tissue at the join between the leader and the leaf stem.

As well as looking a bit “messy” these older leaves that are dying back can be a vector for disease and pests, and often offer an entry point to the rest of the plant. It is good practice to remove them, once they start to look tired. Generally speaking, unless you have a different problem like a mineral deficiency or pest, this won’t happen until the plant has grown substancially, so it isn’t something that should be done until the plant is minimum 3ft tall, and at this stage only the very lowest pair should be removed if they are looking yellow. Some people will argue that energy can still be generated from those leaves, and while that may be true in small amounts, my experience is that it is not enough to significantly effect the growth of the plant, or flavour of the tomatoes.

Indeterminate tomatoes grown without sideshoot removal, supported on cattle panel fencing. Grown by Samantha Schaeffer, Illinois.

Showing 6ft plants, with the lowest 1ft of leaves removed, due to age and to improve airflow

Plants above 1m or so can happily grow with 50% of their leaves removed, but they will grow slower, and fruits will have less flavour. A misguided argument I often hear is that the plant is putting its energy into the leaves, instead of the fruit, so remove the leaves to help the plant focus on the fruit. This is demonstably untrue. The more leaves a tomato plant has, the more it can photosynthesise - the process of turning sunlight and carbon dioxide into oxygen and energy. This energy comes in the form of GLUCOSE. That’s right, plants get their energy from sugar. This is why strawberries, plums, and you guessed it, tomatoes, taste better in hotter, sunnier years. When you remove leaves from your tomato plant, you are depriving the fruits of sugar, so it should only be done where necessary!